Phosphorus Dynamics and Availability in the Nearshore of Eastern Lake Erie: Insights From Oxygen Isotope Ratios of Phosphate

Abstract

Blooms of filamentous benthic algae that plagued Lake Erie in the 1950s through 1970s were largely reduced through reductions of phosphorus (P) loading from point sources.Since the mid-1990s, these blooms have returned despite a period of relatively stable external P inputs. While increased loadings of dissolved P have been causally linked to cyanobacterial blooms in some parts of the lake, the impacts of ecosystem changes such as the effect of invasive species on nutrient cycling and availability have not been fully elucidated, leading to uncertainty as to the effectiveness of additional non-point P management actions. Here we use the oxygen isotope ratios (δ 18 O P ) of phosphate in concert with measures of water quality along the northern shore of the east basin of Lake Erie to identify sources and pathways of P cycling and infer potential importance in relation to annual blooms of Cladophora that foul the shorelines of eastern Lake Erie. δ 18 O P data indicate that potential external source signatures are rapidly overprinted by biological cycling of P by the plankton community and that much of the available phosphate in the nearshore waters is derived from hydrolysis of dissolved organic P compounds. Near the dreissenid-colonized lake bed, δ 18 O P was persistently and significantly enriched in 18 O relative to δ 18 O P measured in surface waters and was similar to δ 18 O P of phosphate excreted by dreissenid mussels in incubations. These results implicate dreissenid mussels as key agents in nearshore P cycling and highlight the importance of considering ecosystem changes in the development of nutrient management strategies designed to ameliorate symptoms of eutrophication.

One size does not fit all: Toward regional conservation practice guidance to reduce phosphorus loss risk in the Lake Erie watershed

“…(2016) indicated that there had been no significant change in overall annual TP loads over the past ∼25 yr. However, a profound re‐eutrophication of Lake Erie has occurred since the mid‐1990s, including cyanobacterial blooms in the western basin, hypoxia in the central basin, and resurgence of benthic algae in the eastern basin (Depew et al., 2018; Scavia et al., 2014).…”

“…Although there have been reductions in P loads in some tributaries such as the Detroit River due to improvements by the Great Lakes Water Authority Water Resource Recovery Facility (see Scavia et al, 2019), Maccoux et al (2016) indicated that there had been no significant change in overall annual TP loads over the past ∼25 yr. However, a profound re-eutrophication of Lake Erie has occurred since the mid-1990s, including cyanobacterial blooms in the western basin, hypoxia in the central basin, and resurgence of benthic algae in the eastern basin (Depew et al, 2018;Scavia et al, 2014).…”

“…Lake Erie has a long history of water quality impairment arising from eutrophication. Phosphorus loadings have been a major cause of harmful algal blooms in the shallow western basin, with hypoxia in the deeper central basin and nuisance filamentous algal blooms along the shorelines of the eastern basin (Baker et al., 2014; Depew et al., 2018; Scavia et al., 2014). After dramatic improvements in water quality during the 1980s and 1990s, Lake Erie has undergone a period of “re‐eutrophication” over the last 20 yr (Kane et al., 2014; Michalak et al., 2013; Scavia et al., 2014; Watson et al., 2016).…”

First Measurements on Triple Oxygen Isotopes of Dissolved Inorganic Phosphate in the Hydrosphere

“…Although the methodology for direct determination has been developed in previous studies, , this method has not been widely adopted because of its complicated pretreatment for extracting and purifying phosphate in Org-P. Additionally, as isotopic fractionation factors are functions of the type of enzyme, − the active extracellular enzymes responsible for the remineralization of DIP from Org-P should be clarified. Therefore, it was difficult to fix the δ 18 O value of DIP remineralized from the biosphere in previous studies. ,,, …”

“…Therefore, it was difficult to fix the δ 18 O value of DIP remineralized from the biosphere in previous studies. 10,13,14,29 In addition to δ 18 O, the Δ′ 17 O value [ = ln(δ 17 O + 1) − λ RL ln(δ 18 O + 1), detailed in Section 2.1] has been recently analyzed for some oxygen compounds to clarify the geochemical and biogeochemical processes on earth. 30−35 Substantial efforts to develop methodologies for the accurate and precise measurement of triple oxygen isotopes ( 16 O, 17 36 referred to as "mass-dependent" fractionation.…”